The beneficial ownership can pass when specific steps are taken to vest it in the legatees in advance of residue being ascertained, see CG30910. But this is fairly unusual. Normally vesting will happen when residue is ascertained and we can infer an assent to the vesting of the beneficial interest. Only occasionally will it happen at some later date where the period of administration has to be extended, see CG30920 - CG30922.